Our objective is to understand the controls on 1) the assembly of actin-and myosin-containing structures, and 2) the interaction of actin and myosin. We also wish to determine how these controls relate to external signalling which results in directed cell movement (chemotaxis). Our goals for the current year are to further explore Dictyostelium actin and myosin. Factors present in crude extracts of Dictyostelium which inhibit polymerization of the actin will be purified and characterized. Actin assembly into filaments will be further studied with special emphasis on nucleation sites for filament formation. Phosphorylation of Dictyostelium myosin heavy chain will be investigated to determine the effect on the ATPase activity of the enzyme. The relationship of this phosphorylation to the ability of the amoebae to chemotaxe toward cAMP will be explored.